Isoascorbic acid (erythorbic acid) is a stereoisomer of ascorbic acid (vitamin C) which is used in the U.S.A. as an antioxidant in foods although prohibited in European countries. Concern exists as to whether isoascorbic acid is antagonistic to vitamin C in the human. The overall goal of the proposed research is to determine whether the ingestion of isoascorbic acid in the diet has any beneficial or adverse effects on the human requirement for vitamin C. The goal will be approached through a series of studies with volunteer young women. The subjects will be fed in our experimental kitchen known diets that contain controlled amounts of ascorbic acid and isoascorbic acid. Specific human experiments have been designed to (a) investigate whether or not isoascorbic acid has a "sparing effect" on the vitamin C requirements; (b) determine whether 13C-1-isoascorbic acid is converted by the human to ascorbic acid to provide vitamin C activity; and (c) study with the use of 13C-1-ascorbic acid whether isoascorbic acid ingestion depletes or displaces ascorbic acid in the body. Other human experiments will be conducted on the kinetics of isoascorbic acid to provide information as to how rapidly the compound is absorbed and cleared from the body. Subjects will also be fed diets that incude processed foods known to contain isoascorbic acid. These studies will provide information as to the magnitude of interference of isoascorbic acid present in foods on the assessment of vitamin C status in the human. The controlled dietary studies will contribute information to our limited knowledge on the vitamin C requirement of women. Since studies on the direct effect of isoascorbic acid on the retention of ascorbic acid in organ tissues is not feasible in the human, this aspect will be investigated in the guinea pig. In conjunction with the project, HPLC-amperometric methodology will be developed that will permit the simultaneous measurement of ascorbic acid, dehydroascorbic acid, isoascorbic acid, and dehydroisoascorbic acid in biological specimens and food samples. The methodology will also be applied to a microbiological study to determine whether or not Lipomyces starkeyi is able to biosynthesize ascorbic acid or dehydroascorbic acid.